Laboratory Studies

Laboratory studies generally are not helpful for diagnosis of traumatic brachial plexus injury, though they may be indicated in the routine evaluation of any trauma patient. Electrophysiologic studies are crucial in the management of these injuries, but timing (eg, for wallerian degeneration to occur) must be considered.

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Imaging Studies

Plain radiography

In anteroposterior (AP) chest radiography, specific attention should be directed to the distance between the spinous processes of the thoracic spine and the scapula. If the radiograph is not malrotated, an increase in this distance as compared with the contralateral side may indicate scapulothoracic dissociation (see the image below).

Traumatic brachial plexus injury. Initial anteroposterior chest radiograph of patient involved in accident with 18-wheeled truck. Clavicle fracture observed on initial chest radiograph was important in signaling need for further evaluation of injury because patient was intubated and unresponsive secondary to closed head injury. Scapulothoracic dissociation was suspected on close review of chest CT scan, and brachial plexus injury was noted once patient became responsive.

Computed tomography

Adequate plain radiographs, especially of the odontoid and the cervicothoracic junction, may be difficult to obtain. Computed tomography (CT) of the neck can often be obtained in conjunction with the CT evaluation received by many trauma patients. Plain CT is very helpful in evaluating any cervical fractures and should be obtained if fractures are suspected on the basis of plain radiographic findings. Chest CT may reveal subclavian vessel injuries, scapular fractures, humeral fractures, and thoracic spine fractures (see the image below).

Traumatic brachial plexus injury. Plain CT scan obtained during initial workup of same patient as in preceding image. Fracture of right scapula is visible, as is right pulmonary contusion and significant periscapular swelling. Scapulothoracic dissociation was suspected on basis of clavicle fracture, scapula fracture, brachial plexus palsy, and high-energy mechanism of injury (ie, accident with 18-wheeled truck). CT scan is oblique; high-quality anteroposterior chest radiograph demonstrating lateral displacement of right scapula was obtained later to confirm diagnosis.

Plain myelography

The most reliable indicator of root avulsion is an absent root shadow on plain myelography.
[12] A common sign of a root avulsion is a meningocele at the affected level; hence, myelography may best be delayed for 4 weeks so that any blood clot will not be dislodged by the study and the meningocele can be allowed to form.

CT myelography

The literature is still inconclusive regarding the sensitivity and specificity of CT myelography (CTM), but CTM is being performed more often.
[13] CTM is capable of detecting lower concentrations of contrast medium than standard myelography can. Burge stated that CTM may be better able to reveal small meningoceles, but artifact from surrounding soft tissues may be problematic at the lower cervical levels.
[14]

Magnetic resonance imaging

Magnetic resonance imaging (MRI) is the current criterion standard for visualizing spinal cord injuries, but reports of its utility in evaluating traumatic lesions of the brachial plexus have been sparse. MRI is the only technique that can be used to visualize the postganglionic brachial plexus. Although the impact of MRI on surgical decision-making is yet to be fully defined, it no doubt will play a larger role in the evaluation of the brachial plexus in the future.

Angiography

Other Tests

Sensory nerve action potentials

Sensory nerve action potentials (SNAPs) are very helpful in differentiating preganglionic from postganglionic injuries. If the injury is proximal to the dorsal root ganglion (DRG), no wallerian degeneration occurs, because the sensory axon is intact. Thus, a SNAP observed in a nerve with an anesthetic dermatome confirms a preganglionic lesion. SNAPs are not useful for C5 evaluation, because C5 does not provide a significant contribution to a major peripheral sensory nerve.

Electromyography

In the first week after injury, electromyography (EMG) cannot be used to exclude a complete nerve disruption unless voluntary motor unit action potentials are observed. If no signs of denervation are apparent in a paralyzed muscle by 3 weeks after injury, EMG can be used to confirm neurapraxia.

Somatosensory evoked potentials

Intraoperative somatosensory evoked potentials (SSEPs) are useful in brachial plexus surgery. The presence of SSEPs suggests continuity between the peripheral nervous system and the central nervous system via the DRG. SSEPs are absent in postganglionic or combined pre- and postganglionic lesions.

Traumatic brachial plexus injury. Patient has ptosis and myosis of his right eye secondary to complete lower brachial plexus lesion.

Traumatic brachial plexus injury. Human cadaveric dissection of right brachial plexus shows that clavicle and some soft tissues have been resected. Nerve roots are exiting their respective foramina at right-hand border. Uppermost nerve root observed is C5, with C6, C7, and C8 also visible. Cords of plexus can be observed at left-hand margin. Note axillary artery at bottom.

Traumatic brachial plexus injury. Initial anteroposterior chest radiograph of patient involved in accident with 18-wheeled truck. Clavicle fracture observed on initial chest radiograph was important in signaling need for further evaluation of injury because patient was intubated and unresponsive secondary to closed head injury. Scapulothoracic dissociation was suspected on close review of chest CT scan, and brachial plexus injury was noted once patient became responsive.

Traumatic brachial plexus injury. Plain CT scan obtained during initial workup of same patient as in preceding image. Fracture of right scapula is visible, as is right pulmonary contusion and significant periscapular swelling. Scapulothoracic dissociation was suspected on basis of clavicle fracture, scapula fracture, brachial plexus palsy, and high-energy mechanism of injury (ie, accident with 18-wheeled truck). CT scan is oblique; high-quality anteroposterior chest radiograph demonstrating lateral displacement of right scapula was obtained later to confirm diagnosis.

The authors and editors of Medscape Drugs & Diseases gratefully acknowledge the contributions of previous authors Christopher Chaput, MD, and Robert Probe, MD, to the development and writing of this article.